Many types of plasma material processing methods are widely accepted for semiconductor fabrication and plasma generation including: sputter etching, plasma-enhanced chemical etching, reactive ion etching, plasma-enhanced vapor deposition, ionized sputter deposition and magnetically enhanced plasma etching. Different types of well-known plasma sources are used in these processes such as the popular inductively coupled plasma (ICP) sources as well as others including: capacitively coupled plasma (CCP) sources, microwave plasma sources (including those that utilize the electron-cyclotron resonance for improved efficiency of power deposition into the plasma), surface wave plasma sources, and helicon plasma sources. In many sources, radio frequency (RF) power can be applied to a RF antenna such that process gas supplied to the plasma generating space is excited, disassociated and ionized. This excitation occurs due to a radio frequency electromagnetic field formed by RF currents in the antenna generating the plasma.
The inductively coupled plasma source and antenna geometry are significant factors in determining plasma and processing uniformity inside the chamber. The growing demands for processing larger and larger wafers or LCD (liquid crystal display) substrates and providing higher and higher degrees of plasma uniformity challenge the current ICP type antenna designs and push development of sources.
Traditional spiral RF antennas are becoming too long for larger wafers or LCD substrates and cannot generate uniform plasmas. Furthermore, such RF antennas are unable to provide the required plasma homogeneity in both, flat and dome-shaped, geometries. Problems with RF antennas occur due to the lengthening of antenna elements relative to the electromagnetic wave and because of the standing wave effects. The standing wave effects become stronger during increased frequency operation of increased wafer or substrate size, limiting the RF antenna's area of application and reducing uniformity.
In addition, radially extended RF antennas are becoming non-efficient because they are not able to uniformly cover the entire plasma processing area over the substrate. Area coverage reduces outwardly from the endpoint such that there is satisfactory coverage closer to the center of the antenna, but unsatisfactory coverage between any two radially extending “arms” of the antenna.
The dome-type antennas are similarly unable to perform adequately given the increasing size of the plasma area and substrates.
Finally, the antennas wired around the sides of the vacuum chamber are becoming inefficient because they cannot provide adequate RF fields in the inner half of the plasma volume.
What is required is a redesigned RF antenna apparatus and method for generating more uniform plasma coverage over larger areas.